Your recipe for insect, weed control could be hazardous to corn

You are trying to manage your various risks in crop production, double checking weed and insect management plans. Then suddenly the crop protection chemical industry throws a wide sweeping curve ball that sails past you for a called strike. You didn’t see that one coming and neither did many other farmers who are also planning to use organophosphate soil insecticides for additional rootworm control, along with some of the more popular herbicides. But it turns out that your plan is fraught with peril. Oooops!

You may be like many farmers surveyed by University of Illinois entomologist Mike Gray who reports that over 90 percent of farmers will be using a Bt hybrid to help control corn rootworms. But just to ensure success, Gray says about half of farmers will also be applying a soil insecticide as “cheap insurance.” “From my perspective, the escalation of soil insecticide use along with corn rootworm Bt hybrids has been fueled primarily by concerns about Bt resistance and high commodity prices," he said.

Gray found the use of a soil insecticide, along with a Bt hybrid for rootworm control to be somewhat ironic. He said, "I think it is worth mentioning that one of the key benefits touted concerning the use of Bt hybrids for corn rootworm management was the reduction of soil insecticide use. It is a bit surprising that, 10 years after the first Bt hybrids entered the marketplace for corn rootworms in 2003, a heightened interest in the use of soil insecticides has surfaced in such a significant fashion."

Are you one of those 50 percent of Bt corn growers who will be using a soil insecticide? If so, what is your weed control plan? That is a key question being asked by Aaron Hager, an Illinois weed specialist. He says the use of organophosphate soil insecticides at planting could restrict the option to use some corn herbicides, specifically those that are ALS or HPPD-inhibiting. Both insecticides and herbicides are foreign to a corn plant, which has to metabolize and break down those compounds. But Hager says the ALS and HPPD herbicides are processed by corn in the same way as organophosphates, the plant can be overwhelmed and injury can occur.

If your insecticide is Counter, Thimet, Lorsban, Aztec or Fortress, they will have varying interactions with a wide variety of popular herbicides. Some can be applied jointly without any interaction. However, others will result in unacceptable, temporary, or severe crop injury. Some herbicides can be applied within 45 or 60 days of the insecticide, and some not at all if you want to keep the corn crop.

Hager provides a handy chart that indicates the potential adverse interactions between the organophosphates and the particular herbicides. He strongly suggests consulting the herbicide label and researching current product information before making your final decision.

Killing insects and weeds are one thing, but killing your crop is another.

Summary:

The increasing reliance of soil-applied insecticides as insurance for Bt control of rootworm may increase the potential for crop damage, depending on the class of insecticides used and the corn herbicides also used on the crop. Certain organophosphate insecticides will create potential damage to corn, if ALS or HPPD-inhibiting herbicides are used.